The present invention relates to an electron spin resonance spectrometer (hereinafter referred to as ESR spectrometer) suitable for measurements in a localized area, and more particularly to an ESR spectrometer suitable for non-destructive measurements of the two-dimensional distribution of specified defects in films related to semiconductor electronics or in semiconductor wafers.
FIG. 8 shows the general construction of a conventional ESR spectrometer. Referring to FIG. 8, a resonant cavity 1 is disposed between a pair of magnetic poles 19 of an electromagnet, and is connected to a microwave generator/detector 16, which makes up a spectrometer 17 together with a recorder 15. A current supplied to the electromagnet is controlled by a magnetic field controller 18. The microwave generator/detector 16 can supply the resonant cavity 1 with microwave, and detect a difference in intensity between the microwave introduced into the resonant cavity 1 and the microwave sent back therefrom. Thus, a reduction in microwave intensity due to the absorption in the resonant cavity, is recorded by the recorder 15 as a function of an applied magnetic field. When magnetic scanning is carried out in a state that a sample 5 is placed within the resonant cavity 1, and a change in microwave intensity due to the microwave absorption of the sample 5 is recorded, an ESR spectrum as shown in FIG. 9 is obtained. A resonance magnetic field (namely, a magnetic field, at which a reduction in microwave intensity due to absorption is maximum) varies with the kind of a defect in the sample 5. Hence, the kind of a defect contained in the sample and the number of defects of this kind can be determined from a resonance magnetic field appearing on an ESR spectrum and a reduction in microwave intensity at this resonance magnetic field. As mentioned above, in the conventional ESR spectrometer, the sample 5 is placed within the resonant cavity 1. Accordingly, the detected signal is an integration of contribution from whole region of samples weighted by the microwave magnetic field strength at each portion. A method of obtaining a detection signal from a specified portion of the sample 5 is disclosed in, for example, a Japanese patent application JP-A No. 58-24843. In this method, the resonant cavity has a through hole at the side wall thereof, and a detection signal is obtained only from that portion of a wafer sample disposed on the outside of the side wall which confronts the through hole. When a mechanism for moving the wafer sample is additionally provided, this method can be used for the two-dimensional distribution measurement of magnetization or mobility in materials for magnetic bubble memory.
In the above method, however, the positional resolution in the two-dimensional distribution measurement is determined by the diameter of the through hole. In a case where the microwave has a frequency in the region of X-band, for example, a frequency of 9.5 GHz, the through hole has a diameter of 5 to 10 mm. When the diameter of the through hole is made smaller than the above, the microwave which can reach the sample on the outside of the resonant cavity through the through hole, becomes very weak, and thus the practical detection sensitivity cannot be obtained. Accordingly, the positional resolution in the above method is set to several milimeters, and hence it is impossible to characterize a localized area of an LSI circuit having a structural unit of one micron.